A typical cellular telephone handset has a small display screen for viewing information and a keypad for entering data, such as a telephone number to be called, and to control and select functions to be performed by the handset. Many telephone handsets are designed to receive paging messages, store information in memory, recall information from the memory, and display it on the display screen of the handset, as well as provide for voice telephone communications. Modern telephone handsets have become very small and, as a result, the display screen on such handsets are, accordingly, quite small. As a result, the amount of information that can be displayed in a given instant of time is limited. The small display screens are quite adequate for normal telephone operations, but when the display screen operates to display a received message such as sent with a page or an E-mail message, the size of the screen becomes a handicap because it is inadequate to display enough information at one time. Similarly, the size of the screen becomes a disadvantage when the handset is operated to display maps, pictures or X-ray photographs.
In prior art systems, it has been proposed to implement the keypad for the telephone handset in the form of a touch tone screen and use the touch tone screen thus provided also as a display screen. Such arrangement, however, is somewhat awkward to use because there is still need for key inputs to control the operation of the handset when it is operated in a display mode.
The present invention provides an improved solution to the problem in that it provides two screens, one which would normally function in telephone dialing operations as a display screen and the second screen will implement the keypad in a touch sensitive mode for the telephone dialing operations. The small display screen will be used in telephone dialing operations to display information related to telephone dialing, such as displaying the number to be called. In accordance with the invention, when the handset is being used to display larger amounts of data, the roles of the two screens are reversed. The small screen then becomes a touch sensitive keypad implementing a small number of keys to control the function of the device and the larger screen, which formerly implemented a telephone keypad, then serves the function of displaying information. In this manner, the entire larger screen used to implement the telephone keypad becomes available to display information and enables a larger amount of information to be displayed simultaneously on the screen.